High efficiency hypochlorite anode coating

ABSTRACT

The invention relates to an electrocatalytic coating and an electrode having the coating thereon, wherein the coating is a mixed metal oxide coating, preferably platinum group metal oxides, with or without a valve metal oxide. The electrocatalytic coating can be used especially as an anode component of an electrolysis cell and in particular a cell for the electrolysis of aqueous hypochlorite solutions.

REFERENCE TO RELATED APPLICATION

This application is a continuation of PCT/US2005/03046, filed Jan. 27,2005, the contents of which are herein incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an electrolytic electrode and a mixed metaloxide coating thereon for the generation of hypochlorite.

2. Description of the Related Art

The use of mixed metal oxide coatings for the generation of hypochloriteby electrolyzing brine solutions is widely known in the art.Conventionally, when hypochlorite is manufactured through theelectrolysis of brine, however, the available chlorine concentration ofthe hypochlorite product can be as low as 1 weight percent (wt %) orless. Additionally, current efficiency and electrode lifetimes diminishwhere brine feed solutions are less concentrated (i.e., 10-30 g/l) andthe desired hypochlorite concentrations exceed 8 g/l.

Various solutions have been proposed to achieve high concentrationsodium hypochlorite solutions without deleteriously effecting currentefficiency and electrode lifetime. For example, there has been taught afilter press type electrolytic cell where in sodium hypochlorite isproduced at a reduced cell voltage and improved current efficiency. Theanode in the electrolytic cell consists of a titanium substrate having acoating of a ternary mixture of 3 to 42% by weight platinum oxide, 3 to34% by weight palladium oxide, 42% by weight ruthenium dioxide and20-40% by weight titanium oxide.

There has also been taught an electrode, especially for chlorine andhypochlorite production, comprises an electrocatalyst consisting of22-44 mol % ruthenium oxide, 0.2-22 mol % palladium oxide and 44-77.8mol % titanium oxide. The electrocatalyst may form a coating on a valvemetal substrate and may be topcoated with a porous layer of titanium ortantalum oxide.

A method for manufacturing hypochlorite efficiently using an anodehaving a coating of palladium oxide by 10 to 45 weight %, rutheniumoxide by 15 to 45 weight %, titanium dioxide by 10 to 40 weight % andplatinum by 10 to 20 weight %, as well as an oxide of at least one metalselected from cobalt, lanthanum, cerium or yttrium by 2 to 10 weight haspreviously been described.

It would be desirable to provide an electrode having an electrocatalyticcoating thereon which is capable of providing improved electrodelifetimes and operating efficiencies in electrolyte environments usedfor the generation of hypochlorite from 15-30 grams per liter (g/l) NaClor KCl feed solutions and where desired hypochlorite concentrationsexceed 8 g/l. It would be further desirable to provide such an electrodeat reduced costs as compared to platinum based formulations.

SUMMARY OF THE INVENTION

There has now been found an electrode coating which provides improvedlifetimes while maintaining high efficiencies in electrolytic solutionsfor the generation of hypochlorite. The coating is a mixed metal oxidecoating consisting of combinations of the oxides of palladium, iridium,ruthenium and titanium.

In one embodiment, the invention is directed to an electrode for use inthe electrolysis of an aqueous solution for the production ofhypochlorite, the electrode having an electrocatalytic coating thereon,with the electrode comprising a valve metal electrode base; a coatinglayer of an electrochemically active coating on the valve metalelectrode base, the coating comprising a mixed metal oxide coating ofplatinum group metal oxides and a valve metal oxide, the mixed metaloxide coating consisting essentially of platinum group metal oxides ofruthenium, palladium, and iridium, and a valve metal oxide of titanium;wherein

-   -   a) the molar ratio of the valve metal oxides to platinum group        metal oxides is from about 90:10 to about 40:60;    -   b) the molar ratio of the ruthenium to the iridium is from about        90:10 to about 50:50; and    -   c) the molar ratio of the palladium oxide to ruthenium plus        iridium oxides is from about 5:95 to about 40:60, basis 100 mole        percent of the metals present in the coating;        whereby the electrode operates at a high current efficiency to        produce hypochlorite concentrations of at least 8 grams per        liter.

In another embodiment, the invention is directed to a process for theelectrolysis of an aqueous solution in an electrolytic cell having atleast one anode therein, the anode having an electrocatalytic coatingthereon, the process comprising the steps of providing an unseparatedelectrolytic cell, establishing in the cell an electrolyte containingchloride, providing the anode in the cell in contact with theelectrolyte, the anode having the electrocatalytic coating comprising amixed metal oxide coating of platinum group metal oxides and a valvemetal oxide, the mixed metal oxide coating consisting essentially ofplatinum group metal oxides of ruthenium, palladium, and iridium, and avalve metal oxide of titanium, wherein

-   -   (a) the molar ratio of the valve metal oxides to the platinum        group metal oxides is from about 90:10 to about 40:60;    -   (b) the molar ratio of the ruthenium to the iridium is from        about 90:10 to about 50:50 and    -   (c) the molar ratio of the palladium oxide to ruthenium plus        iridium oxides is from about 5:95 to about 40:60, basis 100 mole        percent of the metals present in the coating;        impressing an electric current on the anode; and oxidizing        chloride at the anode to produce hypochlorite at concentrations        of at least 8 grams per liter.

DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a graph of the current efficiencies for the production ofhypochlorite of the coatings according to the invention and acomparative coating as a function of hypochlorite concentrations.

FIG. 2 is a graph of the lifetime in hours of the coatings according tothe invention and a comparative coating.

DESCRIPTION OF THE INVENTION

According to the invention, an electrode having an electrocatalyticcoating having a high current efficiency at high hypochloriteconcentrations, e.g., >8 gpl (grams per liter) and having a lowelectrode potential and improved lifetimes is provided. In oneembodiment, depending upon the hypochlorite concentration, the currentefficiency will be from about 90% to about 100% over a hypochloriteconcentration of from 16 to 0 grams per liter (g/l). The electrodehaving the electrocatalytic coating described herein will virtuallyalways find service as an anode. Thus, the word “anode” is often usedherein when referring to the electrode, but this is simply forconvenience and should not be construed as limiting the invention.

The electrode used in the invention comprises an electrocatalyticallyactive film on a conductive base. The conductive base may be a metalsuch as nickel or manganese or a sheet of any film-forming metal such astitanium, tantalum, zirconium, niobium, tungsten and silicon, and alloyscontaining one or more of these metals, with titanium being preferredfor cost reasons. By “film-forming metal” it is meant a metal or alloywhich has the property that when connected as an anode in theelectrolyte in which the coated anode is subsequently to operate, thererapidly forms a passivating oxide film which protects the underlyingmetal from corrosion by electrolyte, i.e., those metals and alloys whichare frequently referred to as “valve metals”, as well as alloyscontaining valve metal (e.g., Ti—Ni, Ti—Co, Ti—Fe and Ti—Cu), but whichin the same conditions form a non-passivating anodic surface oxide film.Plates, rods, tubes, wires or knitted wires and expanded meshes oftitanium or other film-forming metals can be used as the electrode base.Titanium or other film-forming metal clad on a conducting core can alsobe used. It is also possible to surface treat porous sintered titaniumwith dilute paint solutions in the same manner.

Of particular interest for its ruggedness, corrosion resistance andavailability is titanium. As well as the normally available elementalmetals themselves, the suitable metals of the substrate include metalalloys and intermetallic mixtures, as well as ceramics and cermets suchas contain one or more valve metals. For example, titanium may bealloyed with nickel, cobalt, iron, manganese or copper. Morespecifically, grade 5 titanium may include up to 6.75 weight percentaluminum and 4.5 weight percent vanadium, grade 6 up to 6 percentaluminum and 3 percent tin, grade 7 up to 0.25 weight percent palladium,grade 10, from 10 to 13 weight percent plus 4.5 to 7.5 weight percentzirconium and so on.

By use of elemental metals, it is most particularly meant the metals intheir normally available condition, i.e., having minor amounts ofimpurities. Thus, for the metal of particular interest, i.e., titanium,various grades of the metal are available including those in which otherconstituents may be alloys or alloys plus impurities. Grades of titaniumhave been more specifically set forth in the standard specifications fortitanium detailed in ASTM B 265-79. Because it is a metal of particularinterest, titanium will often be referred to herein for convenience whenreferring to metal for the electrode base.

Regardless of the metal selected and the form of the electrode base,before applying a coating composition thereto, the electrode base isadvantageously a cleaned surface. This may be obtained by any of thetreatments used to achieve a clean metal surface, including mechanicalcleaning. The usual cleaning procedures of degreasing, either chemicalor electrolytic, or other chemical cleaning operation may also be usedto advantage. Where the base preparation includes annealing, and themetal is grade 1 titanium, the titanium can be annealed at a temperatureof at least about 450° C. for a time of at least about 15 minutes, butmost often a more elevated annealing temperature, e.g., 600° C. to 875°C. is advantageous.

For most applications, it is advantageous to obtain a base with asurface roughness. This will be achieved by means which can includeintergranular etching of the metal, plasma spray application, whichspray application can be of particulate valve metal or of ceramic oxideparticles, or both, etching and sharp grit blasting of the metalsurface, optionally followed by surface treatment to remove embeddedgrit and/or clean the surface, or combinations thereof. In someinstances the base can simply be cleaned, and this gives a very smoothsubstrate surface. Alternatively, the film-forming conductive base canhave a pre-applied surface film of film-forming metal oxide which,during application of the active coating, can be attacked by an agent inthe coating solution (e.g. HCl) and reconstituted as a part of theintegral surface film.

Etching will be with a sufficiently active etch solution to develop asurface roughness and/or surface morphology, including possibleaggressive grain boundary attack. Typical etch solutions are acidsolutions. These can be provided by hydrochloric, sulfuric, perchloric,nitric, oxalic, tartaric, and phosphoric acids as well as mixturesthereof, e.g., aqua regia. Other etchants that may be utilized includecaustic etchants such as a solution of potassium hydroxide/hydrogenperoxide, or a melt of potassium hydroxide with potassium nitrate.Following etching, the etched metal surface can then be subjected torinsing and drying steps. The suitable preparation of the surface byetching has been more fully discussed in U.S. Pat. No. 5,167,788, whichpatent is incorporated herein by reference.

In plasma spraying for a suitably roughened metal surface, the materialwill be applied in particulate form such as droplets of molten metal. Inthis plasma spraying, such as it would apply to spraying of a metal, themetal is melted and sprayed in a plasma stream generated by heating withan electric arc to high temperatures in inert gas, such as argon ornitrogen, optionally containing a minor amount of hydrogen. It is to beunderstood by the use herein of the term “plasma spraying” that althoughplasma spraying is preferred the term is meant to include generallythermal spraying such as magnetohydrodynamic spraying, flame sprayingand arc spraying, so that the spraying may simply be referred to as“melt spraying” or “thermal spraying”.

The particulate material employed may be a valve metal or oxidesthereof, e.g., titanium oxide, tantalum oxide and niobium oxide. It isalso contemplated to melt spray titanates, spinels, magnetite, tinoxide, lead oxide, manganese oxide and perovskites. It is alsocontemplated that the oxide being sprayed can be doped with variousadditives including dopants in ion form such as of niobium or tin orindium.

It is also contemplated that such plasma spray application may be usedin combination with etching of the substrate metal surface. Or theelectrode base may be first prepared by grit blasting, as discussedhereinabove, which may or may not be followed by etching.

It has also been found that a suitably roughened metal surface can beobtained by special grit blasting with sharp grit, optionally followedby removal of surface embedded grit. The grit, which will usuallycontain angular particles, will cut the metal surface as opposed topeening the surface. Serviceable grit for such purpose can include sand,aluminum oxide, steel and silicon carbide. Etching, or other treatmentsuch as water blasting, following grit blasting can be used to removeembedded grit and/or clean the surface.

It will be understood from the foregoing that the surface may thenproceed through various operations, providing a pretreatment beforecoating, e.g., the above-described plasma spraying of a valve metaloxide coating. Other pretreatments may also be useful. For example, itis contemplated that the surface be subjected to a hydriding ornitriding treatment. Prior to coating with an electrochemically activematerial, it has been proposed to provide an oxide layer by heating thesubstrate in air or by anodic oxidation of the substrate as described inU.S. Pat. No. 3,234,110. Various proposals have also been made in whichan outer layer of electrochemically active material is deposited on asublayer, which primarily serves as a protective and conductiveintermediate. Various tin oxide based underlayers are disclosed in U.S.Pat. Nos. 4,272,354, 3,882,002 and 3,950,240. It is also contemplatedthat the surface may be prepared as with an antipassivation layer.

Following surface preparation, which might include providing apretreatment layer such as described above, an electrochemically activecoating layer is applied to the substrate member. As is typicallyrepresentative of the electrochemically active coatings that are oftenapplied, are those provided from active oxide coatings such as platinumgroup metal oxides, magnetite, ferrite, cobalt spinel or mixed metaloxide coatings. They may be water based, such as aqueous solutions, orsolvent based, e.g., using alcohol solvent. However, it has been foundthat for the electrode of the invention, the coating compositionsolutions are typically those consisting of a mixed metal oxide coatingof platinum group metal oxides and a valve metal oxide.

The platinum group metal oxides of the invention preferably comprise,RuCl₃, PdCl₂, IrCl₃, and hydrochloric acid, all in alcohol solution, incombination with a valve metal oxide. It will be understood that theRuCl₃, PdCl₂, IrCl₃ may be utilized in a form such as RuCl₃ xH₂O, PdCl₂xH₂O and IrCl₃.xH₂0. For convenience, such forms will generally bereferred to herein simply as RuCl₃, PdCl₂ and IrCl₃. Generally, themetal salts will be dissolved in an alcohol such as either isopropanolor butanol, all combined with or with out small additions ofhydrochloric acid, with n-butanol being preferred. It will be understoodthat the constituents are substantially present as their oxides in thefinished coating, and the reference to the metals is for convenience,particularly when referring to proportions.

A valve metal component will be present in the coating composition inorder to further stabilize the coating and/or alter the anodeefficiency. Various valve metals can be utilized including titanium,tantalum, niobium, zirconium, hafnium, vanadium, molybdenum, andtungsten, with titanium being preferred. The valve metal component canbe formed from a valve metal alchoxide in an alcohol solvent, with orwithout the presence of an acid. Such valve metal alchoxides which arecontemplated for use in the invention include methoxides, ethoxides,isopropoxides and butoxides. For example, titanium ethoxide, titaniumpropoxide, titanium butoxide, tantalum ethoxide, tantalum isopropoxideor tantalum butoxide may be useful. In one embodiment, the valve metalalchoxide comprises titanium butoxide.

The mixed metal oxide coating of the invention will contain a molarratio of valve metal oxide to platinum group metal oxides of from about90:10 to about 40:60, a molar ratio of ruthenium to iridium of about90:10 to about 50:50 and a molar ratio of Pd:(Ru+Ir) of about 5:95 toabout 40:60. A particularly preferred composition of the mixed metaloxide coating of the invention will contain a molar ratio of titanium toprecious metal oxides of about 70:30 on a metals basis and a molar ratioof Pd:(Ru+Ir) of about 20:80.

The mixed metal oxide coating layers utilized herein will be applied byany of those means which are useful for applying a liquid coatingcomposition to a metal substrate. Such methods include dip spin and dipdrain techniques, brush application, roller coating and sprayapplication such as electrostatic spray. Moreover, spray application andcombination techniques, e.g., dip drain with spray application can beutilized. With the above-mentioned coating compositions for providing anelectrochemically active coating, a roller coating operation can be mostserviceable.

Regardless of the method of application of the coating, conventionally,a coating procedure is repeated to provide a uniform, more elevatedcoating weight than achieved by just one coating. However, the amount ofcoating applied will be sufficient to provide in the range of from about0.05 g/m² (gram per square meter) to about 6 g/m², and preferably, fromabout 1 g/m² to about 4 g/m² based on ruthenium content, as metal, perside of the electrode base.

Following application of the coating, the applied composition will beheated to prepare the resulting mixed oxide coating by thermaldecomposition of the precursors present in the coating composition. Thisprepares the mixed oxide coating containing the mixed oxides in themolar proportions, basis the metals of the oxides, as above discussed.Such heating for the thermal decomposition will be conducted at atemperature of about 450° C. to about 550° C. for a time of from about 3minutes to about 15 minutes per coat. More typically, the appliedcoating will be heated at a more elevated temperature of up to about490-525° C. for a time of not more than about 20 minutes per coat.Suitable conditions can include heating in air or oxygen. In general,the heating technique employed can be any of those that may be used forcuring a coating on a metal substrate. Thus, oven coating, includingconveyor ovens may be utilized. Moreover, infrared cure techniques canbe useful. Following such heating, and before additional coating aswhere an additional application of the coating composition will beapplied, the heated and coated substrate will usually be permitted tocool to at least substantially ambient temperature. Particularly afterall applications of the coating composition are completed, postbakingcan be employed. Typical postbake conditions for coatings can includetemperatures of from about 450° C. up to about 550° C. Baking times mayvary from about 1 hour up to as long as about 6 hours.

The following examples are included to demonstrate particularembodiments of the invention. It should be appreciated by those of skillin the art that the techniques disclosed in the examples which followrepresent techniques discovered by the inventors to function well in thepractice of the invention. However, those of skill in the art should, inlight of the disclosure, appreciate that many changes can be made in thespecific embodiments which are disclosed and still obtain a like orsimilar result without departing from the spirit and scope of theinvention.

EXAMPLE 1

A flat, titanium plate of unalloyed grade 1 titanium, measuringapproximately 0.15 cm thick and approximately 10×15 cm was grit blastedusing alumina to achieve a roughened surface. The sample was then etchedin a 90-95° C. solution of 18-20% hydrochloric acid for 25 minutes.

Coating compositions as set forth in Table 1 were applied to separatesamples measuring 10 cm×15 cm×0.15 cm of Grade 1 titanium which wasprepared by grit blasting with 54 grit alumina. The coating solutionsA-D were prepared by dissolving sufficient amount of metals, as chloridesalts, to achieve the concentrations listed in the table to a solutionof n-butanol and 4.2 vol % concentrated HCl. The compounds used wereRuCl₃, IrCl₃, and PdCl₂ (all hydrated) and titanium orthobutyl titanate.After mixing to dissolve all of the salts, the solutions were applied toindividual samples of prepared titanium plates. The coatings wereapplied in layers by brushing, with each coat being applied separatelyand allowed to dry at 110° C. for 3 minutes, followed by heating in airto 500° C. for 6 minutes. A total of 5 coats was applied to each sample.Samples A-D are in accordance with the invention. Sample E is considereda comparative example. TABLE I Solution Concentration (gpl) SampleCoating Ru Ir Pd Ti A Ru/Ir/Pd/Ti 20.9 20.9 10.5 43.9 B Ru/Pd/Ti 20.910.5 43.9 C Ru/Ir/Pd 20.9 20.9 10.5 D Ir/Pd/Ti 20.9 10.5 43.9 E Ru/Ir/Ti20.9 20.9 43.9 (Comparative)* Salts are chlorides, except Ti, which is Titanium orthobutyl titanate)

The hypochlorite efficiency of the samples was measured in a beaker-cellby immersing an area of 26 cm² into a solution of 28 gpl NaCl with 1 gplNa₂Cr₂O₇ and applying an anodic current of 4.86 amps (0.186 A/cm²). Atitanium cathode was used, spaced 3 mm from the anode. A sample waspulled every 8 minutes and titrated for hypochlorite. The currentefficiencies for the production of hypochlorite as a function ofhypochlorite concentrations are plotted in FIG. 1 and Table II. TABLE IIRu/Ir/Ti Ru/Ir/Pd/Ti Ir/Pd/Ti Ru/Ir/Pd Ru/Pd/Ti (Comparative) NaOClEfficiency NaOCl Efficiency NaOCl Efficiency NaOCl Efficiency NaOClEfficiency (gpl) (%) (gpl) (%) (gpl) (%) (gpl) (%) (gpl) (%) 2.36 88.52.71 103.6 2.49 95.7 2.51 96.6 2.26 86.5 4.78 88.6 5.12 97.1 4.92 93.95.11 97.4 4.43 83.9 7.09 86.9 7.74 96.8 7.39 93.0 7.69 96.8 6.43 80.59.30 84.8 10.27 95.6 9.71 90.9 10.21 95.6 8.31 77.3 11.49 83.0 12.5492.4 11.49 85.3 12.61 93.6 9.80 72.3

The set of samples, A-E, were then operated as anodes in an acceleratedtest as an oxygen-evolving anode at a current density of 10 kA/m² in anelectrochemical cell containing 150 g/l H₂SO₄ at 65° C. Cell voltageversus time data was collected every 30 minutes and the lifetime takenas the inflexion point at which the voltage began to increase rapidly.The results are summarized in FIG. 2 and Table II, normalized for theamount of platinum group metal. Normalization was done by measuring thex-ray fluorescence count for the metal peaks using a Jordan ValleyEX-300 spectrometer with a Rh tube and a 0.15 mm Sn filter. The appliedvoltage was 40 kV (kilivolts) and current was 25 μA. The peaks measuredwere the RuK-alpha, Pd K-alpha and Ir L-beta. The total counts of theRu, Pd and/or Ir were used to normalize the lifetimes.

It is, therefore, evident from the results of Table II that samplesprepared according to the invention have substantially increased currentefficiencies versus the comparison example while improving or meetingthe lifetime as evidenced by the extended time before a significant risein voltage (>1 volt) occurs.

Although the disclosure has been shown and described with respect to oneor more embodiments and/or implementations, equivalent alterationsand/or modifications will occur to others skilled in the art based upona reading and understanding of this specification. The disclosure isintended to include all such modifications and alterations and islimited only by the scope of the following claims. In addition, while aparticular feature may have been disclosed with respect to only one ofseveral embodiments and/or implementations, such feature may be combinedwith one or more other features of the other embodiments and/orimplementations as may be desired and/or advantageous for any given orparticular application. Furthermore, to the extent that the terms“includes”, “having”, “has”, “with”, or variants thereof are used ineither the detailed description or the claims, such terms are intendedto be inclusive in a manner similar to the term “comprising.”

1. An electrode for use in the electrolysis of an aqueous solution forthe production of hypochlorite, said electrode having anelectrocatalytic coating thereon, with said electrode comprising: avalve metal electrode base; a coating layer of an electrochemicallyactive coating on said valve metal electrode base, said coatingcomprising a mixed metal oxide coating of platinum group metal oxidesand a valve metal oxide, said mixed metal oxide coating consistingessentially of platinum group metal oxides of ruthenium, palladium, andiridium, and a valve metal oxide of titanium; wherein (a) the molarratio of said valve metal oxide to said platinum group metal oxides isfrom about 90:10 to about 40:60; (b) the molar ratio of said rutheniumto said iridium is from about 90:10 to about 50:50 and (c) the molarratio of said palladium oxide to ruthenium plus iridium oxides is fromabout 5:95 to about 40:60, basis 100 mole percent of the metals presentin the coating; whereby said electrode operates at a high currentefficiency to produce hypochlorite concentrations of at least 8 gramsper liter.
 2. An electrode according to claim 1, wherein said valvemetal electrode base comprises a valve metal mesh, sheet, blade, tube,punched plate or wire member.
 3. An electrode according to claim 2,wherein said valve metal electrode base comprises one or more oftitanium, tantalum, aluminum, hafnium, niobium, zirconium, molybdenum ortungsten, their alloys and intermetallic mixtures thereof.
 4. Anelectrode according to claim 3, wherein a surface of said valve metalelectrode base comprises a roughened surface.
 5. An electrode accordingto claim 4, wherein said surface is prepared as by one or more ofintergranlular etching, grit blasting, or thermal spraying.
 6. Anelectrode according to claim 4, wherein there is established a ceramicoxide barrier layer as a pretreatment layer on said roughened surface.7. An electrode according to claim 4, wherein the molar ratio ofruthenium oxide to iridium oxide is about 1:1.
 8. An electrode accordingto claim 7, wherein the molar ratio of said platinum group metal oxidesand said valve metal oxide is within the range of from about 4:1 toabout 1:4.
 9. An electrode according to claim 1, wherein said electrodecomprises an anode utilized in the electrolysis of seawater.
 10. Anelectrode according to claim 1, wherein said electrode operates at acurrent efficiency within the range of from about from about 90% toabout 100% over a hypochlorite concentration of from 16 to 0 grams perliter.
 11. A process for the electrolysis of an aqueous solution in anelectrolytic cell having at least one anode therein, said anode havingan electrocatalytic coating thereon, said process comprising the stepsof: providing an unseparated electrolytic cell; establishing in saidcell an electrolyte containing chloride; providing said anode in saidcell in contact with said electrolyte, said anode having saidelectrocatalytic coating comprising a mixed metal oxide coating ofplatinum group metal oxides and a valve metal oxide, said mixed metaloxide coating consisting essentially platinum group metal oxides ofruthenium, palladium, and iridium, and a valve metal oxide of titanium;wherein a) the molar ratio of said valve metal oxides to said platinumgroup metal oxides is from about 90:10 to about 40:60; (b) the molarratio of said ruthenium to said iridium is from about 90:10 to about50:50 and (c) the molar ratio of said palladium oxide to ruthenium plusiridium oxides is from about 5:95 to about 40:60, basis 100 mole percentof the metals present in the coating; impressing an electric current onsaid anode; and oxidizing chloride at said anode to produce hypochloriteat concentrations of at least 8 grams per liter.
 12. A process accordingto claim 11, wherein said chloride electrolyte in said cell comprisesone or more of sodium chloride or potassium chloride.
 13. A processaccording to claim 11, wherein a surface of said anode comprises aroughened surface prepared by one or more steps of intergranularetching, grit blasting, or thermal spraying.
 14. The process of claim 13wherein said anode surface comprises titanium and said electrocatalyticcoating is provided on said titanium member by a procedure includingelectrostatic spray application, brush application, roller coating, dipapplication and combinations thereof.
 15. A process according to claim12, wherein said ruthenium oxide and iridium oxide are present in amolar proportion of from about 1:3 to about 4:1.